Enzymic formation of riboflavin 4',5'-cyclic phosphate from FAD: evidence for a specific low-Km FMN cyclase in rat liver1.
An enzyme activity splitting FAD to AMP and riboflavin 4',5'-cyclic phosphate (4',5'-cFMN), with a Km of 6-8 microM, was partially purified from the cytosolic fraction of rat liver homogenates. 4', 5'-cFMN was characterized by enzyme, HPLC, UV-visible and NMR spectroscopic analyses. The data suggest that a novel enzyme, tentatively named FAD-AMP lyase (cyclizing) or FMN cyclase, is involved. Also, 4',5'-cFMN was hydrolysed to 5'-FMN by a rat liver cyclic phosphodiesterase. The results indicate a novel enzymic pathway for flavins in mammals, and support the biological relevance of 4',5'-cFMN, perhaps as a flavocoenzyme or a regulatory signal.
Fraiz
F J
FJ
Unidad de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Extremadura, Apartado 108, E-06080 Badajoz, Spain.
Pinto
R M
RM
Costas
M J
MJ
Aavalos
M
M
Canales
J
J
Cabezas
A
A
Cameselle
J C
JC
D000249:Adenosine Monophosphate / Q000378:metabolism; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000201:enzymology; D005260:Female; D005486:Flavin Mononucleotide / Q000031:analogs & derivatives* / Q000378:metabolism; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008345:Manganese / Q000378:metabolism; D008956:Models, Chemical; D019761:Phosphorus-Oxygen Lyases; D011755:Pyrophosphatases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
C111331:riboflavin 4',5'-cyclic phosphate; D005182:Flavin-Adenine Dinucleotide; D000249:Adenosine Monophosphate; D008345:Manganese; D005486:Flavin Mononucleotide; D011755:Pyrophosphatases; D019761:Phosphorus-Oxygen Lyases; C111330:FMN cyclase